Copolymers of 2,5-dimethyl-1,5-hexadiene and acrylic esters



' 1,3-butadiene, which-is itself readily polymerizacan be furtherpolymerized or cured with commolecular weight is desired which iscapable of 1 readily copolymerizcd with anon-conjugated diene,specifically 2,5-dimethyl-1,5-hexadiene, to

yleld soluble, unsaturated resins which, unlike the 50 esters andconjugated dienes, my products, posanalogous copolymers of conjugateddlenes, are

' of relatively low molecular weight and display litproportion of theacrylic ester has copolymerized Patented Kev. 2, 1948 I P v I UNITEDSTATES PATENT corotmaas or ak-nnua'rim. -1,s- J

nsxanmm: Aimnoamc as'raas Pliny 0.,l'awney. Pascale, N. 3., udgnor toUnited Btatedltubber Company, New-York, N. Y., a

corporation of New Jersey v W 'No Drawing Application June 29, 1946,

' Serl'alNo. 680,515

c (01, ZOO-84.5) z

creased above approximately 1:9, the amount of My invention is concernedwith a new class I the acrylic ester which can be converted to the ofunsaturated polymeric materials or relatively low molecular weight whichare soluble in a variety of organic liquids and are resistant to furtherpolymerization, although readily con-,,. g vertible to insoluble.infusible products by-copolymerization with reactive compoundscontaining an ethylen'ic linkage C=C More, insolubillzatlon. The acrylicesters copolymerize particularly, my invention relates to soluble,unwith 2. im thyl-L hexadlene in a wide vasaturated copolymers of anon-conjugated dioleriety oi-proportions and it is therefore possible byfinichydrocarbon with an ester of acrylic acid my invention to securecopolymers which, unlike or of an alpha-alkylacrylic acidand anon-enicthose of the pr r rt. contain considerable monohydric alcohol,hereinafter designated as .amounts of the non-conjugateddiene. For exanacrylic ester. My invention further relates to ample. I have found thatI can readily prepare a tity oi. the diene, i. e., a molar ratio of 6:1,or more, essentially all or the acrylic ester can be converted to anunsaturated copolymer without a method for preparing these-soluble,convertible 1 5 copolymer of methyl ac y ate nd e y resins.

It is well-known that the copolymerlzation of an acrylic ester with aconjugated diene such as .l,5-hexadienein which the diene constitutesnearly by weight or the product.

- My'new copolymers range in character from easily comminuted solids toviscous or plastic ble, yields a soluble, unsaturated, rubber-like 2massesdepending upon the relative proportions product oi relatively highmolecular weight which of the reactants and upon the choice of an ap- Yproprlate acrylides'ter. In general, the softening parative ease :to aheatand solvent-resistant points and molecular weights of my cop l mersmaterial, However, in U. S. Patent No. 2,202,846, tend to decrease asthe amount of the non-con- Garvey and Alexander have pointed out that,in 1 jugated dienc in the reactant mixture is incontrast to suchsoluble, unsaturated copolymers creased, a an in rease in the dienecontent of which may contain'as much as by weight of the conjugateddiene, the copolymerizationof an sponding. increase in their hydrocarbonsolubility. acrylic ester with even small amounts or a nonv For anygiven molar ratio of the diene to acrylic conjugated compound such as a1,4-diene (a an ester, copolymers derived iron esters of acrylic typewhich 'itseli possesses little tendency to homopolymerize), results inthe formation of an insoluble, saturated gel. Similarly, Thomas-andSparks have shown in U. S. Patent No. 2,322,073

the, acrylic esters of higher alcohols such as n- 'butanol and n-octanolyield copolymers ofv the X that the copolymerization of an oleflne suchas 35 softer. more plastic type. Pr duct of intermeisobutylene with aslittle as 0.01% of dimethallyl dlate character can besecured bycopolymerizing (2,5-dimethyl-1,fi-hexadiene), leads to the i'orthe dienewith a mixture of acrylicestersorl by mation of an insoluble, rubberymaterial of low alcohol interchange between the copolymerfajndunsaturation and high molecular weight. Such an appr p iate alcohol.Suitable acrylic'esters products are of limited utility in many applica={o for use in my invention are represented}: the tions such as coatingand molding operations type formula CH2=C(.R) CO-' 0R' wh ie where asoluble, fusible, unsaturated resin of low selected from the classconsisting of hy gen and alk'yl, e. g., methyl, ethyl, and R mayetalkyl, e. g., methyl, ethyl, propyl', isopropyl, butyl; "aryl,

being subsequently cured to the insoluble, infusible state by furtherpolymerization. I 5 e. g. phenyl: and aralkyl, e.- g benzyl. Exemplaryof such esters are n-butyl acrylate, methyl'methacrylate, methylacrylate, ethyl methacrylate, methyl ethacrylate, and phenyl acrylate.

In further contrast to the copolymers of'acrylic I have now unexpectedlydiscovered that, contrary to Garvey et al., an acrylic ester can be sessonly a slight tendency to curelto theinsolujble, infusible state evenwhen heated at elevated tle or no rubber-like character. As Garvey etal. temperatures, e, g., 100 C., with peroxide catahave observed,whenthe cross-linking reactant; lysts, although they gradually becomeinsoluble in this case the'idiene, is present in small amounts, and eveninfusible upon pr longed heating, esp,- the copolymer, becomesinsolubleafter a minor cially at temperatures above 250; C. "1Since.:the

therewith. Hence, it was surprising to find that essing temperaturescommonly employed-afor as the molar ratio of the said cross-linkingdiene plastic materials, my products behave, fon'niany to the acrylicester in the reaction mixture-ls into purpo e as solu e, t ermop asticresin and are copclymeric form before gelation is also increased, and-inthe presence of a suflicient quanthe'copolymers is also'accompanied by'acorre-- 'acids and lower alcohols, e. g., methanol and ethanol, will beharder, and higher-melting, while latter temperature isconsiderablyabove thepr'ocuseful as such. In view of the resistance ofmy unsaturated copolymers to further polymerization, it was surprisingto find that they copolymerize so readily with reactive monomerscontaining an ethylenic linkage, e. g., diethyl fumarate, to yieldinsoluble, infusible products. Thus, my invention may be utilized forthe production of either thermoplastic or thermosetting resins.

The preparation of my new copolymers is carried out by heating a mixtureof the nonconjugated diene and an acrylic ester at a temperature in therange irom about 25 C. up to the reflux temperature of the reactionmixture (in the neighborhood of 120 0.), and for. overall economy it ispreferable to operate in the higher part of the range, e. g., 100-120 C.Temperatures above the normal boiling point of the reaction mixture can,of course, be employed, but the necessary pressure equipment entailsadditional expense without offering any marked compensating advantages.

The copolymerization reaction is accelerated by per-oxy compoundcatalysts such as acetyl peroxide, benzoyl peroxide, acetyl benzoylperoxide, succinyl peroxide, and tertiary-butyi hydrogen peroxide.

The course of the copolymerization can be followed by observing theincrease in viscosity of the reaction mixture, and after the reactionhas been halted by cooling, the copolymer can be isolated by distillingofl. any unreacted starting materials or by extracting them with asolvent in which the copolymer is insoluble. If desired, the copolymercan be further purified by dissolving it in 'a solvent such as acetoneand precipi- I tating it with a non-solvent such as a methanolwatermixture. Since my products are readily soluble in the monomeric2,5-dimethyl-1,5-hexadiene, the copolymerizations can be conducted in anexcess of the diene, if desired, for the resulting free-flowingsolutions are easily handled in transfer, mixing, storage, and othermechanical operations to which the copolymers themselves may be lessamenable. Since my copolymers are resistant to further polymerization,they can be, easily recovered from such solutions by heating to distilloff the excess diene.

when freed from solvents my copolymers can be cast or molded in a knownmanner to form rods, blocks, sheets, etc., and in this form they areparticularly useful where clear flexible articles are required. such asfor safety glass interlayers. Alternatively, the copolymers can bedissolved in appropriate solvents and used for coating and impregnatingprocesses. In the preparation of such solutions, it is often unnecessaryto isolate the copolymer from the reaction mixture, for higher-boilingsolvents may be added directly to the crude, copolymerization reactionmixture and unreacted starting materials can be removed by subsequentdistillation of the solution. Suitable dyes, pigments, fillers,plasticizers and resins can be incorporated with my copolymers to modifytheir character for specific applications.'

Where heat and solvent-resistant materials are desired, my products canbe easily converted to the insoluble, infusible state bycopolymerization with reactive compounds containing'an ethyleniclinkage. such as methyl acryiate, diethyl fumarate, diallyl iumarate,etc. My copolymers dissolve readily in a number of these reactiveethylenic compounds to form solutions which can be totally polymerized,leaving no solvent to be evaporated. Many of these solutions display lowviscosities even at relatively high solids content, which propertyrenders them particularly suitable for coating, impregnating and castingcompositions which can be cured to the insoluble, infusible state with aminimum of blowing, shrinking, and distortion. 5

The following examples disclose my invention in more detail; all partsbeing by weightz EXAMPLE 1 To illustrate my discovery that thecopolymerization of 2,5-dimethyi-1,5-hexadiene with an acrylic esterleads to the formation of soluble, polymeric materials, mixtures ofvarious proportions of methyl acrylate and the diene are heated withbenzoyl peroxide at 60 C. to the point of incipient gelation. Thepolymerizations are then halted by cooling and the reaction mixtures arepoured into n-hexane. The precipitated copolymers are further purifiedby solution in acetone and precipitation with n-hexane, and drying toconstant weight in vacuo. The yields of product are then determined.

The data are summarized below in Table I which includes the weights ofthe copolymerizable monomers, of the peroxide catalyst, and of theproducts, as well as the reaction times. For purposes of comparisononly, the polymerization of the diene in the absence of methyl acrylateis also included, to demonstrate that 2,5-dimethyl- 1,5-hexadienepolymerizes with itself only to a negligible extent.

Table 2 ll-Dimcth Reaction Methyl Benzoyl Polymeric Acry iate yl {if ggPeroxide Egg: Product 1 No sign of incipient geiation.

polymer prior to gelation increases with the amount or non-conjugateddiene present in the reaction mixture. Since Example 19 shows that thediene alone possesses only a small tendency to homopolymerize, theincreasing yield-s of copolymer correspond to conversions of increasingamounts of the acrylic ester to the copolymeric form. Example 1! showsthat in the presence of suflicient quantities or the diene, thecopolymerization can be carried to high yields of product withoutinsolubilization.

Exmru: 2

copolymer is isolated from the viscous distillation v residue by theaddition of n-hexane, and the precipitated product is further purifiedby repeated solution inacetone and precipitation with n-hex- .ane. Afterdrying to constant weight in vacuo.

23 parts of a white polymeric solid are obtained which is readilysoluble in acetone, chloroform, benzene, toluene, xylene and allylicalcohols. The

copolymer softens at approximately 45-50' 0.,

' which is insoluble in acetone.

uration in the copolymer which is available for further copolymerizationwith reactive ethyienic compounds.

Seven parts of the copolymer are dissolved in 3.0 parts oi diethyliumarate and heated in a.

mold with 0.5 part of benzoyl peroxide. for 40.

hours at 60 C. and then for twoadditionai hours at 120 C. to yield aclear, flexible product which is insoluble in chloroform and in acetone.

Exmru 3 A mixture of 51.7 parts of n-butyl acrylate, 375.3 parts 012,5-dimethyl-1,5-hexadiene, and 9.0 parts of a 60% solution oi.tertiary-butyl hydrogen peroxide. is heated for 24 hours at-reflux..Aiter'distillation oi the reaction mixture to remove the majorproportion of the unreacted starting materials, the copolymer isprecipitated from the viscous residue by the addition of a mixture or80% by weight of methanol and 01' water.

Further purification is effected by repeated solution in acetone andprecipitation with the methanol-water mixture, and drying in vacuo; 78.1parts of a clear plastic mass are obtained.

Analysis: Found-C, 7316793; H, 10.66%: 10- dine Number 79.4; [1110,0.073.

v The analysis corresponds to a copolymer containing approximately 62.6%by weight of n-butyl acrylate and 37.4% of the diene.

EXAMPLE 4 A mixture of 25.8 parts of isobutyl acrylate,

187.7 parts of 2,5-dimethyl-1,5-hexadiene and 4.48 parts 01 a 60%tertiary-butyl hydrogen peroxide solution is heated at reflux for 24hours. The resulting copolymer is isolated and purified in the manneroi? Example 3 above to yield 44.5 parts of a clear, plastic mass.

Analysis: Found-C, 74.84% H. 11.02%; Iodine number 87.5; [1 10, 0.062.

1 The analysis corresponds to a copolymer containing approximately 57 .3by weight of isobutyl acrylate and 42.7% of the diene.

Eight parts or the copolymer of Example 4 are dissolved in 2.0 parts ofmethyl acrylate and heated in a mold with 0.2 art of benzoyl peroxidefor 15.2 hours at 60 C., and for 2 additional hours at 120 C. to yield aclear, colorless, tough Similarly. a solution of 7.0 parts of thecopolymer in 3.0 parts or methyl acrylate is admixed with 0.4 part ofbenzoyl peroxide and heated for 15.5 hours at 60 0., and then for 2hours at 120 05 C. The resulting product is tough, somewhat flexible,and insoluble in acetone.

While I have shown and described various embodiments of the invention,it is to be understood that the invention is susceptible to thosemodifl- Number cations which appear within the spirit. of the inventionand the scope of the appended claims.

Having thus described my invention, what I.

claim and desire to protect by Letters Patent is:

1. An acetone-soluble unsaturated copoly- 7o product merizate oi2,5-dimethyl-L5-hexadiene and an acrylic ester of the formula 5 where Xis a radical selected from the group consisting of hydrogen andalkyl,.-and Y is a radical selected from the group consisting of alkyl,aryl and aralkyl in which formation'oi copolymerizate each monomer hasparticipated in more than negligible degree from an original-reactionmixture in which the molar ratio of the diene to the acrylic ester isfrom 1: 1 to 6: 1.

2. An acetone-soluble unsaturated copolymerizate oi2,5-dimethyl-L5-hexadiene and 5 methyl acrylate in which formation ofcopolymerizate each monomer has participated in more than negligibledegree from an original reaction mixture in which the molar ratio of thediene to the acrylic ester is from 1:1 to 6:1.

merizate of 2.5-dimethyl-l,5-hexadiene and n- V butyl acrylate in whichformation of copolymerizate each monomer has participated in more thannegligible degree from an original reaction 5 mixture in which the molarratio of the diene to the acrylic ester is from 1:1 to 6:1.

4. An acetone-soluble unsaturated .cOPOlY merizate of2,5-dlmethyl-1,5-hexadlene and iso- 3. An acetone-soluble unsaturatedcopoly-' butyl acrylate in which formation of copoly- 52,5-dimethyl-1,5-hexadiene and a monomeric acrylic ester of the formulax CHFd-QoO-Y where X is a radical selected from the group consisting ofH and alkyl, and Y is a radical selected from the group consisting ofalkyl, aryl and aralkyl, in the presence of a per-oxy compound catalyst,the molar ratio of the diene to the acrylic ester being from 1:1 to 6:1,and stopping the reaction before the mixture gels whereby to produce ahigh yield of an acetone-solubleinterpolymerizate of said monomers.

6. A method which comprises heating together 2,5 dimethyl-1,5-hexadieneand a monomeric acrylic ester of the formula CHF-COO--Y where X is aradical selectedfrom the group consisting of H and alkyl, and Y is aradical selected from the group consisting of alkyl, aryl and REFERENCESCITED The following references are of record in the file of this patent:

UNITED: STATES PATENTS Name Date Garvey et al. June 4, 1940 OTHERREFERENCES Norrish et al., Proceedings Royal Society London (1937);,41-163, pp. 205-1220.

